Metal coating of light metals



March 3, 1959 R. 1.. DOERRV I 2,876,138

METAL comma OF LIGHT METALS Filed April 14. 1953 APPLY T0 In: usm' METALT0 as COATED A SOLUTION or A mun: couwousm I.E.,

(a) A MIXTURE OF STANNOUS CHLORIDE AND A PYRAZOLINE HYDROHALIDE OR (b) AZINC CHLORIDE COMPLEX SALT OF A PYRAZOLINE HYDROHALIDE,OR

(cI'AMIXTURE or In) ANIHbI AND (2) A nn nocen SALT conrousru' I .E.,

(a) A l-IYDRAZl NE HYDROHALIDE ,on

(b) A MIXTURE OF A HYDRAZINE HYDROHALIDE AND AN AMMONIUM HALIDE',

IN A SOLVENT CARRIER.

HEAT THE LIGHT METAL COATED WITH THE SOLUTION TO PRODUCE THE METALCOATING.

Richard L. Doerr INVENTOR.

ATTORNEYS United States Patent METAL COATING OF LIGHT METALS Richard L.Doerr Niagara Falls, N. Y t on]. Mnthieoon Chcmical Corporation, 3corporation of Application April 14, 1953, Serial No.-348,822

16 Claims. (Cl. 117-130) My invention relates to an improved process ofapplying continuous metal coatings to light metals and their alloys.More particularly, my invention relates to the coating of aluminum andits alloys containing high proportions of aluminum with zinc and tin andzinc-tin alloys.

Protective metal coatings may be applied to light metals and theiralloys by electroplating from suitable solutions, by dipping the lightmetals in molten metals, for example, zinc, or in molten salts, forexample, zinc chloride, or by dusting the light metal with powderedmetals or their salts and subsequent heating. The light metals may alsobe dipped into various aqueous solutions in order to deposit aprotective coating of heavier metal on the light metal. In general,electroplating is more expensive than dipping methods of applying metalcoatings since the same amount of metal must be provided as well as theadded cost of the required electrical energy. In the dipping processes,however, adequate adherence of the metal coating to the light metal isfrequently diflicult to obtain. Moreover, in known processes the lightmetal must be subjected to extensive preliminary cleaning operations.

I have now found that applying certain solutions, containing asessential ingredients a metal halide component, a pyrazoline hydrohalideand a nitrogen salt component, to light metals, for example aluminum,and heating the light metal with its coating of solution produces evencontinuous metal coatings on the light metal. Extensive preliminarycleaning operations are eliminated and very adherent coatings of theprotective metal are obtained at low cost. The metal halide componentmay comprise a zinc halide, e. g. zinc chloride, or a tin halide, e. g.stannous chloride, or both a zinc halide and a tin halide, e. g., zincchloride and stannous chloride, in any relative proportions. Zincchloride and stannous chloride are preferred because of their relativecheapness as compared to other halides. The nitrogen salt componentcomprises a hydrazine hydrohalide or a mixture of ahydrazine hydrohalideand an ammonium halide.

According to the process of my invention, I apply the solutions to alight metal, e. g. aluminum and aluminum alloys, in any suitable manner,for example, dipping or brushing. The metal with its coating of solutionis then heated, for example, to about 400 to 450 C., and the reaction isusually continued until the evolution of fumes ceases and an evencontinuous metal coating of zinc or zinc-tin is obtained on the surfaceof the .light metal. With the process of my invention no extensivepreliminary cleaning operation is needed and very adherent coatings areobtained. t I

The pyrazoline hydrohalides useful in the coating compositions areadvantageously obtained by the reaction of an aldehyde or a ketone withhydrazine and hydrogen halide as described in my pending applicationSerial No. 348,823, filed April 14, 1953, now Patent No. 2,801,195. Thecompounds may be formed by separately reacting the aldehyde or ketonewith hydrazine followed by reacthe hydrogen halide.

2,876,138 Patented Mar. 3, 1959 tion with the selected hydrogen halideor the compounds may be formed by reacting the aldehyde or ketone with ahydrazine monohydrohalide. Substituted hydrazines and hydrazinehydrohalides may be employed. For example, dimethyl hydrazine, phenylhydrazine, hydroxy ethyl hydrazine or the hydrohalides thereof maybeemployed. The useful hydrogen halides include hydrogen fluoride,hydrogen bromide and hydrogen chloride, but I prefer compositions basedupon hydrogen chloride. Suitable aldehydes and ketones that may be usedto produce the pyrazoline hydrohalides are those containing at least onealpha hydrogen. At least one alpha hydrogen must be present in thecarbonyl compound in order to effect ring closure to-form thepyrazoline. For best results in application to metal coating operationsthe nature of the'organic radical should be selected to avoid excessivecarbonization during the coating operation. Thus aldehydes or ketones ofgood thermal stability provide suitable materials in the preparation ofmetal coating compositions.

I have found that pyrazoline hydrohalide compounds prepared from ketoneshave particular value in the coating compositions of my invention. Thepyrazoline prepared from acetone, i. e. 3,5,5trimethylpyrazoline-hydrohalide, is particularly advantageous, butpyrazolines prepared from other lower aliphatic ketones such as methylethyl ketone, diacetone alcohol, diethyl ketone and methyl isobutylketone are also useful. In addition, methyl vinyl ketone, aldol, mesityloxide and methyl phenyl ketone can be employed in producing pyrazolinehydrohalides which have value in coating compositions. Among thealdehydes, acetaldehyde, propionaldehyde, butyraldehyde, acrolein andcrotonaldehyde may be employed.

In the preparation of the pyrazoline compounds, when saturated carbonylcompounds are used, preferably two moles or more of the aldehyde orketone may be reacted with one mole of the hydrazine monohydrohalide byadmixture at ordinary temperatures or with application of controlledheat. When certain unsaturated aldehydes or ketones, such as acrolein orcrotonaldehyde, are used, one mole of the aldehyde or ketone is reactedwith one mole of the hydrazine monohydrohalide. of viscous or solidmaterials, an inert solvent is employed. The product may be recovered inthe usual way by crystallization and filtration from the excess aldehydeor ketone or the reaction medium. Alternatively, the aldehyde or ketonemay be reacted with hydrazine, either as a solution of the .hydrate orin the anhydrous state, and the resulting reaction mixture is furtherreacted with aqueous or gaseous hydrogen halide. Again the reactingproportions are two moles or more-of the saturated aldehyde or ketone,or one mole of the unsaturat'edfor each mole of hydrazine to be reactedand one mole of The compounds prepared from the aldehyde or ketone,hydrazine and the hydrogen halide are advantageously recrystallized rommethanol or other suitable solvent in order to obtain a purifiedproduct.

In the stannous chloride compositions, the stannous chloride andpyrazoline hydrohalide are mixed in proportions of from about 10 toweight percent of either component. Compositions of this type aredescribed in my pending application Serial No. 348,824, filed April 14,1953, now Patent No. 2,801,196. The stannous chloride and pyrazolinehydrohalide are then mixed with the nitrogen salt component to form themetal coating compositions.

In the zinc chloride compositions, zinc chloride and a pyrazolinehydrohalide are mixed and the resulting product is then mixed with thenitrogen salt component to form the metal coating compositions.Compositions of In the caseth'n type are described in my pendingapplication Serial No. 348,821, filed April '14, 1953, now Patent No.2,801,194. The zinc chloride is believed, on the basis of experimentalfindings, to form a complex salt with the pyrazoline hydrohalide. Thezinc chloride and pyrazoline components alternatively may be obtainedfrom zinc chloride, an aldehyde or a ketone and a hydrazine hydrohalide,reacted in any order, or fromzinc dihy'drazine chloride, a ketone or analdehyde and a hydrogen halide. The reaction is spontaneous andexothermic and advantageously provision is made for the dissipation ofthe heat of the reaction.- Advantageously, the ketone or aldehyde may beadded at a suitable rate to a mixture of zinc chloride and a hydrazinehydrohalide under reflux in order to avoid loss of ketone or aldehyde.Suitable proportions are about 2 moles of ketone or aldehyde: to 1 moleof hydrazine hydrohalide. From about 0.5 to 1 mole of zinc chloride isused per mole of hydrazine hydrohalide. Water may be added to thereaction mixture to control the heat of reaction. Alternatively, thehydrazine hydrohalide and zinc chloride in aqueous solution may be addedto .the' ketone -or aldehyde. For example, an aqueous solution of 20moles of hydrazine hydrochloride and moles of zinc chloride in 1.33 kg.of water was added to 40 moles of acetone under reflux. From theresulting solution, a crystalline product was obtained having a meltingpoint of l47'-151' C. Elementary analyu's for all of the elementspresent corresponds to the theoretical for a complex of 2 moles of 3,5,5trimethyl pyrazoline monohydrochloride and l fmole of zinc chloridehaving the formula:

When alloy coatings are desired, a mixture of a zinc halide and a tinhalide is used with the pyrazoline hydrohalide and the nitrogen saltcomponent. The relative proportiom of zinc chloride and stannouschloride are such as to provide an alloy coating of the desiredcomposition. Thus, when a coating of approximately 70 percent zinc am!30 percent tin is desired, the proper proportion of zinc chloride tostannous chloride is approximately 3:1.

'l1se nitrogen salt component of the metal coating compositionscomprises a hydrazine hydrohalide or a mixture of a hydrazinehydrohalide and an ammonium halide.

. Of the hydrazine hydrohalides, hydrazine hydrochloride is preferred asthe cheapest and most readily available of these salts of hydrazinealthough hydrazine hydrobromide may be used. Of the ammonium halides,ammonium chloride is preferred'for the same reason to other ammoniumsalts, such as ammonium bromide. Ammonium chlorideis much cheaper thanhydrazine hydrochloride and high proportions of the ammonium chloride tohydrazine hydrochloride are preferred. The ratio by weight may rangefrom 1:1 to 5:1 or more. Distinctly less satisfactory coatings areobtained, however, when smaller proportions of hydrazine hydrochlorideare used. Except for the cost, hydrazine hydrochloride could besubstituted entirely for ammonium chloride. Some ammonium chloride ispreferred in the composition, however, asit improves fluidity at coatingtemperatures. The nitrogen salt component may comprise about 10 topercent of the weight of the metal halide component.

The-stannous chloride compositions may be used in solutions of loweraliphatic monohydric alcohols, e. g.

methanol, ethanol, the propanols or the butanols, and lower aliphaticdihydric alcohols, e. g. ethylene glycol, propylene glycol or butyleneglycol, or mixtures thereof. Methanol is preferred as the compositionsare more soluble therein and more concentrated solutions may beprepared. The zinc chloride. compositions may be used in solutions oflower aliphatic monohydric alcohols, e. g. methanol, ethanol, thepropanols or the butanols, lower aliphatic dihydric alcohols, e. g.ethylene glycol, propylene glycol or butylene glycol, water or mixturesthereof. Water is preferred as it is cheaper and avoids fire hazards.The proportion of solvent to the metal halide, pyrazoline hydrohalideand nitrogen salt components is advantageously the minimum necessary todissolve these components and provide a clear solution. Advantageously,solutions containing about 20 to 50 percent solids may be used.

The process of my invention and preferred solutions will be furtherillustrated by the following examples:

Example I An aqueous solution of 1.36 kg. of zinc chloride and 1.37 kg.of hydrazine hydrochloride in 1.33 kg. of water was added to 2.32 kg. ofacetone at a rate causing the acetone to reflux. The reaction wascompleted without additional heat. be the zinc chloride complex of 3,5,5trimethyl pyrazoline monohydrochloride.

An aluminum sheet was coated with a mixture of 50 parts by weight of thereaction product, 5 parts of ammonium chloride, 1 part of hydrazinehydrochloride and 50 parts of water and heated to about 400-450 C.Heating was continued until the solvent evaporated and the reaction wascontinued until the evolution of fumes ceased. An even coating of zincon the aluminum resulted.

When the reaction product was used alone, excessive charring occurredand very poor coatings of zinc were formed.

Example 11 A composition similar to that of Example I can prepared fromstannous chloride, 3,5,5 trimethyl pyrazoline monohydrochloride,hydrazine hydrochloride and ammonium chloride dissolved in methanol. Theresulting solution can be used in the procedure of Example I to producean even coating of tin on an aluminum sheet.

The method of my invention will be further illustrated by the flowdiagram of the drawing. In the drawing the solution of the halidecomponent, (i. e., a mixture of stannous chloride and a pyrazolinehydrohalide, or a zinc chloride complex salt of a pyrazoline hydrohalideor mixtures thereof) and the nitrogen salt component (i. e., a hydrazinehydrohalide or a mixture of a hydrazine hydrohalide and an ammoniumhalide) in a solvent carrier is applied, e. g., by dipping or brushing,to the light metal surface and the light metal with the coating ofsolution is heated, e. g., to about 400 to 450 C., and the reactioncontinued usually until the evolution of fumes ceases and an evencontinuous coating of metal is obtained on the light metal surface.

I claim:

1. In the process of applying continuous even coatings of metals tolight metals by applying a solution of a metal salt to the light metaland heating the metal to a temperature and for a time sutlicient to coatthe metal, the step of applying to the light metal to be coated asolution which consists essentially of (1) a halide component selectedfrom the group consisting of (a) a mixture of about 10 to weight percentof stannous chloride and about 10 to 90 weight percent of a pyrazolinehydrohalide, (b) a zinc chloride complex salt of a pyrazolinehydrohalide, and (0) mixtures of (a) and (b), and (2) about 10 to 50weight percent based on the stannous chloride and zinc chloride of anitrogen salt component selected from the group consisting of ahydrazine hydrohalide and a mixture of a hydrazine hydrohalide and anammonium halide, the halide in said hydrazine hydrohalide and ammoniumhalide being se- The reaction product was believed to.

lected from the group consisting of chloride and bromide, said metalhalide, pyrazoline hydrohalide and nitrogen salt component beingdissolved in a compatible solvent.

2. In the process of applying continuous even coatings of metals tolight metals by applying a solution of ametal salt to the light metaland heatingthe metal to a temperature and for a time suflicient to coatthe metal, the step of applying to the light metal to be coated asolution which consists essentially of (1) a mixture of about to 90weight percent of stannous chloride and about 10 to 90 weight percent ofa pyrazoline hydrohalide and (2) about 10 to 50 weight percent based onthe stannous chloride of a nitrogen salt component selected from thegroup consisting of a hydrazine hydro halide and a mixture of ahydrazine hydrohalide and an ammonium halide, the halide in saidhydrazine hydrohalide and ammonium halide being selected from the groupconsisting of chloride and bromide, and a carrier selected from thegroup consisting of lower aliphatic monohydric alcohols and loweraliphatic dihydric alcohols.

3. The process of claim 2 in which the light metal is aluminum and itsalloys.

4. The process of claim 2 in which the pyrazoline is selected from thegroup consisting of pyrazoline, lower alkyl substituted pyrazolines,phenyl substituted pyrazolines and pyrazolines substituted with loweralkyl and phenyl substituents.

5. The process of claim 2 in which the pyrazoline hydrohalide is3,5,5-trimethyl pyrazoline hydrochloride.

6. The process of claim 2 in which the solution consists essentially ofa methanol solution of stannous chloride, a pyrazoline hydrochloride,hydrazine hydrochloride and ammonium chloride.

7. In the process of applying continuous even coatings of metals tolight metals by applying a solution of a metal salt to the light metaland heating the metal to a temperature and for a time suflicient to coatthe metal, the step of applying to the light metal to be coated asolution which consists essentially of (1) a zinc chloride complex saltof a pyrazoline hydrohalide and (2) about 10 to 50 weight percent basedon the zinc chloride of a nitrogen salt component selected from thegroup consisting of a hydrazine hydrohalide and a mixture of a hydrazinehydrohalide and an ammonium halide, the halide in said hydrazinehydrohalide and ammonium halide being selected from the group consistingof chlohols and lower aliphatic dihydric alcohols.

8. The process of claim 7 in which the light metal is aluminum and itsalloys. x

9. The process of claim 7 in which the pyrazoline is selected from thegroup consisting of pyrazoline, lower alkyl substituted pyrazolines,phenyl substituted pyrazolines and pyrazolines substituted with loweralkyl and phenyl substituents.

10. The process of claim 7 in which the pyrazoline hydorhalide is3,5,5-trimethyl pyrazoline hydrochloride.

11. The process of claim 7 in which the solution consists essentially ofan aqueous solution of a zinc chloride complex salt of a pyrazolinehydrochloride, a hydrazine hydrochloride and ammonium chloride.

12. In the process of applying continuous even coatings of metals tolight metals by applying a solution of a metal salt to the light metaland heating the metal to a temperature and for a time suflicient to coatthe metal, the step of applying to the light metal to be coated asolution which consists essentially of (1) a mixture of (a) a mixture ofabout 10 to weight percent of stan nous chloride and about 10 to 90weight .percent of a pyrazoline hydrohalide and (b) a zinc chloridecomplex salt of a pyrazoline hydrohalide and (2) about 10 to 50 weightpercent, based on the stannous chloride and zinc chloride of a nitrogensalt component selected from the group consisting of a hydrazinehydrohalide and a mixture of a hydrazine hydrohalide and an ammoniumhalide, the halide in said hydrazine hydrohalide and ammonium halidebeing selected from the group consisting of chloride and bromide, and acarrier selected from the group consisting of lower aliphatic monohydricalcohols and lower aliphatic dihydric alcohols.

13. The process of claim 12 in which the light metal is aluminum and itsalloys.

14. The process of claim 12 in which the pyrazoline is selected from thegroup consisting of pyrazoline, lower alkyl substituted pyrazolines,phenyl substituted pyrazolines and pyrazolines substituted with loweralkyl and phenyl substituents.

15. The process of claim 12 in which the pyrazoline hydrohalide is3,5,5-trimcthyl pyrazoline hydrochloride.

16. The process of claim 12 in which the solution consists essentiallyof a methanol solution of stannous chloride, a pyrazoline hydrochloride,a zinc chloride complex salt of a pyrazoline hydrochloride, hydrazinehydrochloride and ammonium chloride.

Merenoescltedintheflleotthispatent UNITED STATES PATENTS

12. IN THE PROCESS OF APPLYING CONTINOUS EVEN COATINGS OF METALS TOLIGHT METALS BY APPLYING A SOLUTION OF A METAL SALT TO THE LIGHT METALAND HEATING THE METAL TO A TEMPERATURE AND FOR A TIME SUFFICIENT TO COATTHE METAL, THE STEP OF APPLYING TO THE LIGHT METAL TO BE COATED ASOLUTION WHICH CONSISTS ESSENTIALLY OF (1) A MIXTURE OF (A) A MIXTURE OFABOUT 10 TO 90 WEIGHT PERCENT OF A STANNOUS CHLORIDE AND ABOUT 10 TO 90WEIGHT PERCENT OF A PYRAZOLINE HYDROHALIDE AND (B) A ZINC CHLORIDECOMPLEX SALT OF A PYRAZOLINE HYDROHALIDE AND (2) ABOUT 10 TO 50